Grassy surfaces across Chicago have taken on a burned-out appearance and gardeners are noticing cracks in once waterlogged ground. As remarkable as it seems, given the incredibly wet start to this year’s growing season, the area is dry and in need of rain. It’s not an unusual problem this time of year. Summer sunlight is so intense moisture problems often arise at this point in the season. A week of normal rainfall this time of year sees 1.05 inches fall; that’s short of the 1.52 inches required to replenish moisture lost through evaporation. Not only has rainfall the past three weeks not come close to normal, totaling a paltry 0.28 inches (just 11 percent of the long-term average), the just completed mid-July to early August period has been the driest in 63 years. The situation may turn around—and quickly in some locations—as thunderstorms erupt ahead of this weekend’s blast of heat. Rainfall is unevenly distributed in the warm season because so much of it is generated by thunderstorms, which concentrate downpours over comparatively small area.
The atmospheric setup that appears to be coming together Friday and Saturday will see the air’s moisture content surge past 2 inches—as much water as the atmosphere holds here. At the same time, the flood of hot air into the Chicago area may well destabilize the atmosphere, encouraging air to rise. It’s a setup known to produce thunderstorms. The wild card will be whether the depth of the hot air grows quickly to the point that a storm-thwarting “cap,” i.e. layer of warm air, develops aloft and retards storm development. That may happen Sunday—but could permit storm development ahead of the hottest air’s arrival Friday afternoon into Saturday morning–and perhaps over parts of the metro area Saturday afternoon and evening.
How does the cool summer of 2009 compare to other recent cool summers we’ve endured, such as 2004 and 1992?
Tim Lucole, Deerfield
With an average temperature of 70.0 degrees as of July 31, it’s certainly accurate to characterize this summer as “cool.” In fact, it ranks 8th coolest out of 82 years of temperature data (1928-2009) at Midway Airport.
However, this might be a premature characterization because meteorological summer runs through August 31 and one-third of the season is yet to occur. It’s difficult to keep temperatures down in August. Indeed, a pattern change suggests much higher readings in a few days.
From June 1 through July 31, this summer’s daily high temperatures have averaged 78.1 degrees (versus a normal of 82.7 in that period) and it ranked third coolest; 2004 (79.6 degrees) was 8th coolest and 1992 (78.8) was 4th coolest.
Dave Skrzyniarz sends us these photo. In the e-mail accompanying it, Dave tells us:
“Strange pics on Monday at 4:30—-a jet left this trail thru the cloud deck—it actually looked like it emerged from the clouds and left this mark. Several other jets also had the same effect — making the clouds appear to be smoke!”
Fascinating shot, Dave—THANKS for sharing it with us!
Photos courtesy of Dave Skrzyniarz
Powerful thunderstorms sweep into the Peoria area–part of a Tuesday outbreak which produced damaging winds, flooding rains from Missouri to Kentucky
Thunderstorms unleashed 60 to 70 m.p.h. wind gusts on sections of downstate Illinois and Indiana as well as Missouri and Kentucky Tuesday morning. Rob Shreiner, a paramedic with photographic skills evident in this set of photos, sends us these eye-catching shots of the ominous skies which accompanied the storms as the roared into the Peoria area. Rob tells us:
“I was in Peoria, IL this morning as this storm rolled in at approx 8:36 AM today.
Amazing formations as they were rolling down at me as I was taking the images. Gusts present and the heavy rain did not begin until approx 10 minutes after this came in.
Only adjustments were auto contrast, slight sharpen and obviously crop, all taken w/ 16-35mm wide angle lens, so that’s why all the poles tilt inward.”
Thanks for sharing these with us, Rob!
Photos courtesy of Rob Schreiner, Wadsworth, Illinois
The moderate warmth that has dominated so much of Chicago’s summer 2009 to date continues another two days. Wednesday and Thursday highs are to reach the lower 80s. But, big changes loom this weekend as long absent heat begins its charge into the Chicago area on 30+ m.p.h. wind gusts which are expected to be in place here Saturday afternoon and like to continue Sunday. The rapidly expanding dome of hot air threatens ignite clusters of active thunderstorms to the west of Chicago over sections of the Plains and western Midwest in coming days. These storms may sweep into the Chicago area Friday night into Saturday morning. The cool outflows which occur with such storms must always be monitored–they’ve been known to interfere with hot air’s movement. But, with the incoming hot air mass expected to become “capped” and unable to produce thunderstorms here Saturday afternoon and evening, mid 90s seem a good bet before the sun sets Saturday and readings may even increase to the upper 90s Sunday. Temperatures at that level this weekend would be the warmest here in three years and mark the first time a weekend has produced back to back 90+-degree highs in just over two years.
Powerful storms storms topple trees, power poles downstate; Kentucky hit by 6-inch-plus rains
The veil of high clouds across the Chicago area Tuesday blew off the tops of powerhouse thunderstorms responsible for damaging winds and driving rains from northern Missouri across central and southern Illinois and Indiana. Gusts to 67 m.p.h. raked Indianapolis and hit 66 m.p.h. in west Lafayette in Indiana. In downstate Illinois, gusts of 60 m.p.h. swept Springfield while Lincoln and Mattoon recorded 55 m.p.h. gusts and Bloomington was swept by 49 m.p.h. gusts. Utility poles and trees snapped at many locations. Meantime, rainfall reached 6.46 inches at Grand Rivers, Kentucky and Louisville’s 4.52 inches was a record calendar day rain for the month of August.